Gearboxes are currently not used only to provide different gears during operation of an engine in order to be able to optimise fuel consumption and operating characteristics, as it is also possible to connect extra equipment to a gearbox. Extra equipment herein means any equipment not driven by the output shaft of the gearbox, such as a power take-off or a supplementary brake, especially a retarder. Electric motors may also be connected to the gearbox to achieve hybrid operation. These examples are particularly relevant to the operation of heavy utility vehicles, e.g. trucks.
A gearbox is provided with a main gear unit comprising a mainshaft and, parallel with it, a countershaft, and is also often provided with a range gear unit, e.g. a planetary gear, which can be put into a low-range gear state and a high-range gear state. The range gear unit can be put into a neutral state in which the output shaft is disconnected from the mainshaft so that the power-transmitting connection between the two shafts is broken. The mainshaft is connectable to an input shaft of the gearbox via the countershaft and to an output shaft of the gearbox via the range gear unit. A gearbox of this type may also be provided with a split gear unit via which the countershaft of the main gear unit is connectable to the gearbox input shaft.
One of the gears in the gearbox is intended to impart to the mainshaft an opposite direction of rotation to that of the engine's output shaft. If the gearbox is installed in a motor vehicle, this causes the vehicle to move rearwards. Accordingly, the gearwheel on the mainshaft will then not be in direct engagement with the corresponding gearwheel on the countershaft, but will be driven by an intermediate gearwheel which, during reversing of the vehicle, is in engagement with both of them. The mainshaft gearwheel, intended to run in the first direction of rotation, will then have an opposite direction of rotation than the other gearwheels on the mainshaft during operation, since the direction of rotation of the mainshaft gearwheel will have been changed once across the intermediate gearwheel. The mainshaft gearwheel which is intended for operation in the first direction has teeth angled in the opposite direction to teeth on the gearwheels which are intended for operation in the second direction.
WO 2004/069624 refers to a vehicle transmission in which a supplementary brake, e.g. a retarder, may be situated either immediately after the clutch (see FIG. 2 thereof) or immediately before the range gear (see FIG. 7 thereof) along the path of power delivery. The retarder is connected via a separate clutch (34, 90) which connects the retarder (56) to the gearbox mainshaft via gearwheels (32, 50).
SE525612 refers to a power take-off connected to gearbox gearwheels. FIG. 2 thereof shows the power take-off's gearwheel (6) connected to a gearwheel (23) on the countershaft (24). The specification indicates that a gearwheel (21) on the mainshaft (22) is in engagement with a countershaft gearwheel.
Disadvantages of the state of the art comprise the fact that energy losses occur when extra equipment is not being used, since the whole or parts of it are continually driven by the gearbox, and/or that the connection for extra equipment occupies space. The mainshaft gearwheel for driving the mainshaft in the first direction also causes energy losses during operation in the second direction because of being continually forced to rotate in an opposite direction. All forms of energy loss tend to increase fuel consumption.
For example, a hydrodynamic retarder consumes a relatively large amount of energy even when it is not being used, since the retarder housing can never be completely emptied of oil used for retarding. The retarder is therefore constantly forced to operate against a certain resistance.
Similar problems to those with the retarder also affect other forms of extra equipment, e.g. a power take-off for a mobile crane. Although there may be a coupling between the mobile crane and the power-transmitting means which is connected to gearwheels of the gearbox, the power-transmitting means will still be forced to operate even if the coupling to the mobile crane is not activated.
It is for various reasons currently desired to keep down the number of components used in vehicle manufacture. This is not only to make it possible to reduce costs by having as few components as possible both in production and in spare parts storage but also to facilitate assembly. A consequence of this endeavour is that components cannot be allowed to be freely changed in size and shape. For example, it is desired to have no more variants of gearbox housings than necessary, so the connection of extra equipment to a gearbox has therefore to be accommodated within the existing gearbox housing. A motor vehicle today consists of many components which have to share a limited amount of space on the chassis, making it impossible for their size and shape to be altered freely. For the above reasons it is very important to be able to modify the gearbox without its having to occupy extra space. It is therefore desirable to obviate the prior art requirement for space for connecting extra equipment to the gearbox.